Senate Minority Leader Charles Schumer (D-N.Y.) on Saturday said Republican lawmakers' efforts to uncover the identity of an FBI informant in order to obstruct special counsel Robert Mueller's investigation comes close to "crossing a legal line."

Schumer was tweeting his support of a statement from the Senate Intelligence Committee's top Democrat, Mark Warner (Va.), who warned Republican lawmakers against exposing the identity of the informant who gave investigators information about possible ties between the Trump campaign and Russia.

Warner said in a separate Twitter thread on Friday, "It would be at best irresponsible, and at worst potentially illegal, for members of Congress to use their positions to learn the identity of an FBI source for the purpose of undermining the ongoing investigation into Russian interference in our election."

Exposing sources "makes it that much harder for every part of the intelligence community to gather intelligence on those who wish to do us harm," Warner wrote.

The next day, Schumer said Warner's statement was "on the money" and serves as a severe warning to GOP representatives who are trying to tamper with the investigation.

Schumer and Warner's comments come after a report from The Washington Post alleged President Trump had begun a campaign to expose the role of the informant.

The Justice Department (DOJ) denied a request earlier this month from House Intelligence Committee Chairman Devin Nunes (R-Calif.) for details related to the source. The DOJ said that releasing such information would put lives at risk and endanger national security.

On Saturday afternoon, the president responded to the news, tweeting, "if the FBI or DOJ was infiltrating a campaign for the benefit of another campaign, that is a really big deal." Trump concluded by calling for the Justice Department to release the documents Nunes requested.